docs: def twoaxes(self, y):
          """Cigtab test objective function"""
          X = [y] if isscalar(y[0]) else y
          N2 = len(X[0]) // 2
          f = [1e6 * sum(x[0:N2]**2) + sum(x[N2:]**2) for x in X]
          return f if len(f) > 1 else f[0]